The present invention relates to mass spectrometers and in particular to a high-resolution detector for time of flight spectrometers.
Mass spectrometers are analytic instruments that may provide for the precise measurement of the mass of molecules. Generally, the molecules to be measured are given an electrical charge and then accelerated by an electrical field. The velocity of their acceleration will be generally proportional to the mass to charge ratio (m/z) and so for a given and known charge the mass may be precisely determined by a velocity measurement.
One method of determining velocity is the use of a “sector” type analyzer which bends the trajectories of the charged particles using a magnetic field. When the particles exit the magnetic field, the angle of their trajectories (and spatial separation at a measurement point) will be in proportion to m/z and may be measured by a series of spatially separated collectors.
An alternative detection system uses a “time of flight” analyzer in which relative velocities of different molecular species are deduced based on the time it takes them to reach a detector. Common detectors used for time of flight analysis include so-called “Faraday cups” which are conductive metal cups, which catch charged particles and are attached to sensitive electrical amplifiers and “dynode” detectors which provide an amplification of received charge through electron multiplier techniques.
Mass spectrometry is increasingly applied to extremely large molecules, for example proteins, that may be ionized by various techniques such as matrix assisted laser desorption/ionization (MALDI) in which the fragile proteins are protected with a matrix material that is struck by a laser beam. The matrix absorbs the energy of the beam and is removed from the protein while transferring a charge to the protein.
The large mass of protein molecules decreases the sensitivity of a time of flight spectrometer to the extent that the velocity of the proteins is lower and thus the difference between velocities of similar masses is less. This requires that the difference in measured times of flight must be resolved more precisely. Conventional spectrometer detectors can exhibit latencies that hide small mass differences for large molecules thus limiting the mass resolving power of the spectrometer.